Brain-machine interface is a direct communication and control path established between human brain and computer or other electronic devices. Through this path, one can express himself or operate apparatus directly by his activity of brain without speaking or actions of his limbs.
Different from ordinary man-machine interfaces, a brain-machine interface does not need muscular responses of any type, but merely detects the signal representing responsive or purposeful activity of brain.
A control device based on brain-machine interface may achieve the purpose of controlling a target apparatus without one's speaking or actions of limbs.
Different from subjective sense organ testing systems, an objective sense organ testing system based on brain-machine interface does not need speaking or actions of limbs of the person to be tested for expressing his subjective consciousness, but merely detects the signal representing responsive or purposeful activity of his brain. Thus the system can provide objectivity and justness.
The followings are some existing methods of performing brain electrical signal control.
1. The Method Based on Event Related Brain Electrical Signal
For instance, prior to starting an autonomic motion, there exists so-called event related desynchronized component associated with the motion in one's brain electrical signal, which is substantially an evoked brain electrical signal. We may identify the event related signal in the recorded brain electrical signal, and use the same for performing a certain kind of control.
Pfurtscheller et al. carried out a series of BCI (Brain-Computer Interface) research on the basis of such physiological phenomenon. A subject (testee) faced an object displayed on the right or left of a display, and prepared to press a button with his (or her) left or right forefinger according to the object's position. Then after about one second, there appeared a cross cursor at the center of the display. The subject pressed the button. The brain electrical signals used for classification are those appeared in the activity preparing phase between the appearance of the object and the appearance of the cursor. In this way, a template was obtained through learning, whereby the activity of right hand or left hand could be predicted. (“Brain-computer Interface—A New Communication Device foe Handicapped Persons”, J Microcomput Appl, 1993, 16:293–299; “Prediction of the Side of Hand Movements from Single Trial Multichannel EEG Data Using Neural Networks” Electroenceph Clin Neurophsiol, 1992, 82:313–315).
2. The Methods Based on Evoked Electrical Brain Signal
FIG. 1 is a schematic drawing that depicts a prior art system carrying a certain kind of control based on evoked brain electrical signal. The steps of this method comprises: giving a subject some stimulus; recording and identifying the brain electrical signal evoked under various stimuli; and performing a certain kind of control by virtue of the identified signal.
P300 is a kind of event related potential (EPR). A peak value will appear in brain electrical signal in 300 ms after the occurring of the related event, which is called as P300. Farwell and Doncin designed a virtual printer by virtue of EPR. A 6*6 character matrix scintillates randomly by row or column, and the scintillating of the row or column containing the character to be entered by the user is the related event. Find out the row and column causing the maximum amplitude of P300, then the character on the intersecting point of the row and the column is the character to be printed.
Sutter's BCI system utilizes visually-evoked potential (VEP) method. A 8*8 symbol matrix on a display appears as red/green alternation in a pseudo-random binary order. The user looks at the character to be chosen, compares the detected brain electrical signal with a prerecorded template, then may confirm the target at which the user is looking. Previously learning to obtain a steady template is a critical step (“The Brain Response Interface: Communication through Visually-evoked Electrical Brain Response”, J Microcomput Appl, 1992, 15:31–45).
The above system utilizes instantaneous evoked response. As the basis of the testing is P300, so it is required that the time interval between two stimuli to be more than 1 second, so as to ensure that the response of the subject to the preceding stimulus has ended or disappeared before the arrival of a new stimulus. Thus, the system cannot be used for real-time control, and the reliability of the test cannot fulfill practical requirement too.
Up to date, another primary disadvantage of brain-machine interface method as one of testing technique is the lack of ability to give sense organ stimulus mode with space information simultaneously. Thus, there is no space resolution information of sense organ system in the testing result, so the scope of application is greatly limited.